Ascertainment of Secondary Cases of Hepatitis A -- Kansas, 1996-1997

Each year, 25,000-30,000 cases of hepatitis A are reported in the United States. The most common infection source (22%-26%) is household or sexual contact with a person already infected with hepatitis A virus (HAV) (i.e., the source-patient) (1). In Kansas during 1992-1997, contact with a source-patient was reported by 39% of persons with hepatitis A (2). Cases reported in 1996 and 1997 were studied retrospectively to determine the reasons for the apparently high proportion of secondary cases and to evaluate missed opportunities for prevention (i.e., postexposure prophylaxis with immune globulin [IG]) (3,4). Results of this investigation indicate that persons with hepatitis A often were classified incorrectly as secondary cases and that some correctly identified secondary cases represented missed opportunities for prevention.

For this investigation, the hepatitis A cases included were those the Kansas Department of Health and Environment determined as being secondary and were among the residents of one of the five Kansas counties reporting the highest number of secondary cases each year during 1996-1997. Kansas counties collected information using CDC's Viral Hepatitis Surveillance Program form, which includes whether case-patients reported "sexual, household, or other contact with a suspected or confirmed hepatitis A case within the 2-6 weeks before onset of their illness." Persons who responded affirmatively to this question were classified as having a secondary case for the Kansas Annual Summary of Reportable Diseases (2).

As part of this investigation, the definition of a secondary case was expanded to include persons reporting any contact with a source-patient and with an illness onset of either 15-65 days after onset of illness in the source-patient or, in the case of a single exposure to the source-patient, 15-50 days after that exposure date. Persons with an illness onset date within 15 days of illness onset in the source-patient were presumed to be co-infections and classified as concurrent primary cases. When the interval between the onset dates of source and presumed secondary case was greater than 65 days, they were considered unrelated. Information on each case-patient was obtained from data recorded on the surveillance form and from on-site review of local health department records.

During 1996-1997, the state recorded 655 persons with hepatitis A; 443 (68%) were from the selected counties. Of these 443 cases, 210 (47%) had been classified as secondary cases: 16 (8%) reported sexual contact, 66 (34%) reported household contact, 104 (54%) reported "other" contact, and 24 (4%) had no type of contact recorded.

Of the 210 patients originally classified as having secondary cases, 119 (57%) had illnesses that met the investigation definition of a secondary case, 53 (25%) were reclassified as having co-primary cases, and seven (3%) were reclassified as having unrelated cases. For 27 (13%) patients, information was insufficient to determine when contact had occurred, and information for four (2%) had been entered incorrectly in the database.

According to recommendations for postexposure prophylaxis used in Kansas, 53 (45%) of the 119 secondary case-patients should have been offered IG. Of these, 18 (34%) received IG, seven (13%) were offered IG but refused, and 26 (49%) were identified too late to provide effective postexposure prophylaxis: 15 (28%) had not been reported as contacts by the source-patient, and for 11 (21%) a source-patient either was not reported or was reported after the secondary case was diagnosed. For two (4%) patients, the reason for not being offered or receiving IG was unknown.

Among the 18 patients who developed a secondary case of hepatitis A, the median interval between source-patient diagnosis and receipt of IG by the secondary case-patient was 7 days (range: 0-15 days), within the recommended interval of 2 weeks from last exposure. However, the median interval between receipt of IG by the secondary case-patients and the subsequent onset of illness was 11 days (range: 3-34 days), suggesting that the patients were late in their incubation period when they received IG. Twelve (67%) of these patients were household contacts and three (17%) were day-care contacts, all of whom had multiple exposures to their source-patients over days or weeks during the infectious period.

Sixty-six (55%) of the 119 secondary case-patients did not meet criteria for receiving IG; among them likely sources of infection could be identified for 44 (67%): seven (11%) occurred during a school-associated outbreak, and 37 (56%) reported close personal contact with a source-patient. Circumstances of these contacts, which had not been reported during the original investigation, included 15 (23%) secondary case-patients who had used illegal drugs and 22 (33%) secondary case-patients who had participated in activities (such as playing; sharing drinks, ice, or meals; or providing care for a person) with hepatitis A.

Editorial Note:

This investigation illustrates that assessing specific aspects of surveillance data, such as case investigations, data collection, and analysis can identify areas in need of modification or improvement. Accurate and understandable case definitions are needed to classify primary and secondary cases of hepatitis A; also, timely and complete case reporting and investigations are necessary to avoid missing opportunities for prevention.

In Kansas, the high proportion of reported secondary cases occurred because some of these cases should have been classified as co-primary or unrelated cases. The proportion of reported cases that met the definition used in this investigation (27%) is consistent with that reported nationwide (1). To improve the accuracy of surveillance data, health department personnel should verify that both the presumed source and presumed secondary case-patient meet the hepatitis A case definition, that close personal contact has occurred, and that the interval between illness onset in the source and in the secondary case-patient was 15-50 days, the hepatitis A incubation period.

The limitations of this investigation relate to its retrospective design. The data used had been previously collected for surveillance purposes and not specifically for this investigation. Because the patients were not reinterviewed, additional information about the type of contact with the potential source-patients was not collected systematically and sometimes was not available.

The Advisory Committee on Immunization Practices recommends IG for persons who have been exposed to HAV and have not been vaccinated (5). IG should be given as quickly as possible after exposure, but not longer than 2 weeks after the last exposure. Situations in which IG is recommended include close personal contact with a person with hepatitis A, including household and sexual contacts; contact with HAV-infected persons in day-care centers, and sometimes following exposure to a foodhandler with hepatitis A (5). Hepatitis A vaccination is recommended for preexposure prophylaxis in certain populations and settings, but is not approved for postexposure prophylaxis (5).

Approximately 25% of persons who had had household or sexual contact with a source-patient were identified too long after exposure to benefit from IG. Health departments should encourage rapid laboratory reporting of positive serologic test results and should educate health-care providers about the importance of complete and timely reporting. Local health department personnel also should be encouraged to conduct prompt and thorough case investigations to identify contacts for whom IG might be indicated.

Another 30% of secondary cases occurred among persons who had no household or sexual contact with a person with hepatitis A but had reported other types of close personal contact that have been associated with transmission, such as contact with young children with unrecognized infection, and participating in the practices associated with illegal drug use (6-10). The risk for and the mode of transmission in these circumstances have not been established and are difficult to assess. An evaluation of the characteristics of each contact should be conducted to identify exposed persons who are not household or sexual contacts. Persons who report other types of close personal contact with a hepatitis A patient should be considered candidates for IG. Studies to characterize features of exposures associated with HAV transmission are needed to develop explicit criteria for IG administration in these settings.

DisclaimerAll MMWR HTML versions of articles are electronic conversions from ASCII text
into HTML. This conversion may have resulted in character translation or format errors in the HTML version.
Users should not rely on this HTML document, but are referred to the electronic PDF version and/or
the original MMWR paper copy for the official text, figures, and tables.
An original paper copy of this issue can be obtained from the Superintendent of Documents,
U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800.
Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to
mmwrq@cdc.gov.